1. Field of the Invention
The present invention relates to an image taking system and a lens apparatus which have a ranging function.
2. Description of the Related Art
In a live telecast of marathon, the distance between a top runner and a second runner is often announced. The distance between the runners at this time may be a rough distance which has been measured by eye of an announcer or a reporter, or may be a distance which has been calculated by using the time from the top runner has passed through until the second runner passes through a certain point and the running velocity of each runner. Therefore, the distance between the runners given by the announcer or the reporter is not precise. Further, viewers can not visually recognize the distance by just being given to the viewers by the announcer or the reporter.
Japanese Patent Laid-open No. 2003-329915discloses an image taking system as described below. First, a focusing is manually performed for a first object, and a distance to the first object is calculated based on a position of a focus lens at the time of being in an in-focus state. Next, similarly to the case of the first object, a focusing is manually performed for a second object, and a distance to the second object is calculated based on a position of the focus lens at the time of being in the in-focus state. Then, the difference between the calculated first and second object distances is obtained to superimpose the difference information with a video signal to display it.
Japanese Patent Laid-open No. 6-331883 discloses a ranging system as described below. The ranging system irradiates light for ranging to a plurality of objects corresponding to a plurality of ranging points, and calculates a distance to the object at each ranging point by receiving reflected light from each object. Further, the plurality of ranging points are divided into a plurality of groups based on distributions of the positions and the calculated distances. A group which has a size smaller than a predetermined size among the plurality of groups are regarded as an in-focus state group, and a focus control is performed based on the calculated distance of the in-focus state group.
However, in an image taking system disclosed in Japanese Patent Laid-open No. 2003-329915, in order to calculate the distances of the first and second objects, a focusing has to be performed for each of the first and second objects. In other words, the distance to the second object can not be calculated while the in-focus state for the first object that is a main shot target is maintained.
In the image taking system, since the distance between both objects is obtained after the distance to the first object is calculated and the focusing is performed for the second object, a real distance between the objects may change before the distance between the objects is obtained. In other words, when the real distance between the objects changes from moment to moment in a marathon race or the like, the distance between the objects which rapidly reflects the changes can not be calculated.
In a ranging system disclosed in Japanese Patent Laid-open No. 6-331883, it is possible to calculate the object distances at the plurality of ranging points regardless of the current in-focus state. However, it is necessary to select a targeted object out of the plurality of ranging points. In addition, in the ranging system, although one group is selected out of a plurality of groups, at least two objects (runners) needs to be selected in performing a distance display in a marathon live or the like. Further, it is often the case that a person who is not a runner or an object that has a size similar to a person, other than a main object that is a runner, is shot at the same time. Therefore, it is difficult to determine whether or not it is the main object (runner) based on the size of the group.